To provide a concrete, albeit non-restricting example, problems underlying the invention are described in connection with electrical drives that provide vertical movement or movement with a vertical component, such as electrical cranes, hoists or lifts. This is because the load being lifted or suspended affects the entire system of gears, axles and bearings, even in a steady-state condition when motion is stopped. A safety brake is typically installed on the primary or engine side of the gear. If the gear breaks catastrophically, free fall of the load is possible. Those skilled in the art will realize, however, that early prediction of gear failure is desirable in connection with virtually any electrical drives, regardless of direction of motion.
In the context of the present invention, prediction of gear failure comprises two tasks, namely monitoring gear condition and detecting potentially risky changes in the gear condition.
JP05069923B2 discloses techniques for a hoist crane with a diagnosis apparatus that calculates diagnosing value of abrasion of gear wheel based on variations in electric current flowing into motor and rotation angle value of shaft when gear wheel meshes with a motor. An operation control apparatus controls drive of an electric motor and a rotation angle detection apparatus linked to rotating shaft of the motor. A current sensor measures variation in electric current flowing into the motor and the rotation angle detection apparatus detects variation in rotation angle of the shaft when the gear wheel meshes with motor. An abrasion diagnosis apparatus calculates diagnosing value of abrasion of gear wheel based on variations in electric current value and rotation angle value.
A problem with the prior art is the extensive instrumentation required to measure the currents and to detect the various rotation angles with sufficient precision, resolution and repeatability. While it may be feasible to provide new equipment with such additional sensors and connections, retrofitting existing equipment is difficult, labor-intensive and expensive.